This invention relates to a pulsating hearth for an incinerator, and is more particularly directed to such a hearth which is capable of concurrent intermittent moving and stoking of a pile of random size particles burning on the hearth.
Incineration may provide acceptable means for disposing of waste, for heat processing of various materials, and for recovery of heat from burning refuse; however, the process of incineration has had imposed upon its use severe and substantial limitation. Some incinerators requires removal of materials not fully combustible in prior art systems or burnable only with undesireable side effects or hazards; thus a sorting step is necessary for use of such processes and equipment. Other incinerators need shredded material for burning and that prerequisite also requires extra processing and equipment. Most prior art incinerators are incapable of meeting environmental standards, and require one or more of a wide range of auxiliary equipment, such as afterburners, scrubbers, precipitators and the like to make them function.
Even with suitable pre-incineration processes and equipment and auxiliary environmental protection devices, full combustion of random refuse material is seldom achieved, because adequate oxygenation of the burning particles is required, although the burning cannot be so rapid as to make the fire too hot or permit excessive gasification or atomization of the burning particles or the products of combustion. Optimum non-polluting combustion requires close control of the time, turbulence and temperature of the burning process. The problem is further magnified when the refuse contains plastics, wet refuse and liquids and when unburned particles are permitted to escape from the main burning chamber.
Preferably the main burning chamber of an incinerator has a hearth floor. However, such a hearth has some inherent problems requiring solution for effective and efficient combustion of random refuse. The refuse on the hearth must receive an even distribution of oxygen for the material to burn. Air must be mixed with the burning material and dispersed. Air alone, particularly with high velocities, will entrain and lift burning particles before they are fully consumed. The uncontrolled rapid burning of the pile may also increase velocities. Such high velocities and the accompanying incomplete burning results in slagging and tends to clog up the incinerator floor, as well as to permit incompletely burned particulate and products of combustion to exit the main burning chamber of the incinerator before they are adequately consumed.
Some incinerators have been constructed using a starved air principle in their main burning chamber, but in these devices the lack of oxygen does not permit the burning of hydrocarbons to convert to water and carbon dioxide, thus carbon monoxide is frequently formed, representing a hazard to operating personnel and restricting use of such devices to very well ventilated areas.
Additionally, it is often desired to control the rate and extent of the burn in the main combustion chamber, without either the risk of pollution or the loss of desired selected unburned or ash products. For example, in some incinerator processes it is desired to burn perhaps 75% of each particle, but no more, and return the mostly burned particles before it is entirely reduced to ash. In other processes, it is desired to burn off readily combustible coatings and retain substrata unburned and not damaged by heat. In these situations it is particularly useful to control both the rate of burning and the time that the particle to be burned is subject to the heat of combustion.